A shuttle bus driver who police said fatally shot a colleague Friday at the former Walter Reed Army Medical Center told authorities that the victim had moments earlier punched him so hard that several of his teeth fell out, according to newly filed court documents.

The suspect, Wright Koonce, 59, who has addresses in Silver Spring, Md., and Falls Church, Va., said that after he was struck, he grabbed a .38-caliber revolver and shot the victim as he ran "with his back to him," the arrest affidavit says.

Police said Koonce then stood over Brian Andre Gibson, 45, and fired another shot. He reloaded his revolver but did not fire again because the victim was not moving, the affidavit says.

Koonce told police that he feared for his life and fired at the fleeing Gibson "because he did not know what the decedent was going to do," according to the affidavit.

Koonce was charged Saturday with second-degree murder while armed. A D.C. Superior Court judge ordered him detained until a preliminary hearing Jan. 4.

In a statement Friday, police had reversed the order of the suspect's name, erroneously identifying him as Koonce Wright.

The shooting occurred about 8 a.m. Friday just inside the gated entrance to the old Army complex on Georgia Avenue between Brightwood and Shepherd Park in Northwest Washington.

Police said in the affidavit that Koonce and Gibson worked for G&M Limo Service, which shuttles workers from a parking lot near the Georgia Avenue entrance to a construction site. Walter Reed is being redeveloped into a residential and retail complex. Representatives for the limo company could not immediately be reached for comment.

Relatives of Koonce and Gibson could not be reached for comment Monday. Koonce's attorney did not respond to messages. Gibson lived in an apartment across the street from the Walter Reed complex.

Police said without elaborating that the men had argued about transporting the construction workers.

Koonce told detectives, according to the affidavit, that he retreated to his vehicle in the lot but that Gibson followed, opened the driver's side door and beat him. Koonce said he grabbed his gun, got out of the vehicle and shot Gibson as he fled.

The two were about seven feet apart when the first shot was fired, according to police.

A witness told police that he saw Koonce walk to a guard shack and "just stood by and waited for the police to arrive, without uttering any words," the affidavit says.